245/50R20 tyre size
A 245/50R20 tyre is 245 mm (9.6") wide with a sidewall height of 50 % of the width, i.e. 122.5 mm (4.8"), on a 20" (508 mm) rim. Overall diameter is 753.0 mm (29.6"), so the closest inch-style size is 29.6×9.6R20. Static circumference is 2366 mm; the ETRTO rolling circumference is 2297 mm, giving 435 revolutions per km (701 per mile).
Dimensions and rolling diameter
| Section width | 245 mm | 9.65″ |
| Sidewall height | 122.5 mm | 4.82″ |
| Rim diameter | 508.0 mm | 20″ |
| Overall diameter (static, unloaded) | 753.0 mm | 29.65″ |
| Static radius | 376.5 mm | 14.82″ |
| Static circumference (π × D) | 2,366 mm | 93.1″ |
| Rolling circumference (ETRTO 3.05 × D) | 2,297 mm | 90.4″ |
| Effective rolling radius | 365.5 mm | 14.39″ |
| Revs per km (rolling / static) | 435 / 423 | |
| Inch equivalent | 29.6×9.6R20 | |
| Approved rim widths (approx.) | 6.5″–8.5″ (measuring rim 7.5″) | |
A 245/50R20 tyre is 245 mm (9.6") wide with a sidewall height of 50 % of the width, i.e. 122.5 mm (4.8"), on a 20" (508 mm) rim. Overall diameter is 753.0 mm (29.6"), so the closest inch-style size is 29.6×9.6R20. Static circumference is 2366 mm; the ETRTO rolling circumference is 2297 mm, giving 435 revolutions per km (701 per mile).
Why two circumferences? The static figure is simple geometry (π × diameter). Under load a radial tyre flattens and rolls about 3 % less per revolution; ETRTO defines the rolling circumference as 3.05 × the nominal diameter, which is what manufacturers quote and what speedo and gearing calculations should use.
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